Key questions about the incident are still unanswered and no group has claimed responsibility.

The Russian Ministry of Defense has acknowledged an attack on its Khmeimim air base in Syria, but has disputed key details from an initial report, denying that seven aircraft had been destroyed in the incident. At the same time, unconfirmed pictures have begun emerging on social media showing significant damage to at least one Su-24 Fencer attack plane.

On Jan. 4, 2017, the Russia’s Ministry of Defense, by way of state-run media outlet TASS, said militants had attacked Khmeimim, also known as Hmeimim or Hmeymim, and killed two Russian service members in the process. The Kremlin did not say if there were any other casualties, but insisted that earlier reports that the assault had destroyed seven aircraft were categorically false. On Jan. 3, 2017, independent Russian daily Kommersant had reported this detail and that the enemy force had wounded 10 individuals, citing unnamed diplomatic sources.

"On December 31, 2017, at nightfall, the Hmeymim airfield came under a sudden mortar fire from a mobile militant subversive group,” the Russian Ministry of Defense said, according to TASS. “A report in the Kommersant newspaper on the alleged destruction of seven Russian warplanes at the Hmeymim airbase is fake. Russia’s air group in Syria is combat ready and continues to accomplish all its missions in full.”

It is important to note that this denial does not say militants were not successful in destroying any aircraft, just that the report of seven aircraft destroyed in total is inaccurate. And the reported loss of aircraft would hardly render the Russian air contingent in Syria combat ineffective.

According to Kommersant, militants had destroyed four Su-24 Fencer attack planes, two Su-35S fighter jets, and an An-72 tactical transport. Past satellite imagery has shown as many as six Su-35s and nearly a dozen Su-24s, along with a variety of other fighter and ground attack aircraft, such as the very active Su-25 Frogfoots, on the ground at the base.

As we at The War Zone have already noted, this imagery also shows the aircraft parked very close together without any defensive bulwarks between them. As such, it is not at all implausible that a very limited attack could have set off a chain reaction of sorts leading to a number of aircraft ending up with severe damage. Live munitions have also often been seen stored in close proximity to tactical aircraft at the base.

Additional unconfirmed reports and images have begun to appear on social media, most notably a post from war correspondent Roman Saponkov on the site VKontakte, or VK, a Russian-language analogue to Facebook. His post indicated that as many as a dozen of Russia’s fixed wing aircraft and helicopters had ended up with at least some damage, but that at least some of the Su-24s and Su-35s were back in action.

Saponkov attached a set of photos that appear to show an Su-24 armed with live bombs and leaking fluid from where a piece of shrapnel had punctured the fuselage. Other pictures show the mangled tail section of an Su-24.

The jet’s tail number, White 29, is reportedly the same as an aircraft that deployed from Shagol air base in Russia to Syria in the past. The images show a rainy environment, and the local weather has included precipitation as of late, and especially on the next morning following the attack.

Significant questions about the incident still remain, however. Khmeimim is situated deep inside territory that Syrian dictator Bashar Al Assad and his Russian and Iranian allies firmly control and rebel groups and terrorists lack the means to strike the site directly from areas in which they operate freely. The lack of revetments or other defenses at the base separating individual aircraft would seem imply that the Russians felt the site was essentially immune to a direct assault.

To launch an attack with a mortar, the type of weapon that both Kommersant and TASS said militants used in the incident, would require the enemy force to get deep into a regime area, and near the highly patrolled air base itself, without detection.

Aside from the primary narrative that this was an indirect fire attack, another possibility is that rebels or terrorists used a small quad- or hex-copter style drone with an improvised payload to launch the attack remotely. ISIS has already demonstrated this capability in both Iraq and Syria. There have also been rumors that Russian-backed insurgents in Eastern Ukraine, or the country’s own security services, used a very similar tactic to launch a devastating attack on an ammunition dump in the Ukrainian city of Balakliya.

On the other hand, we do know that the base is defended by a very dense air defense network, including Pantsir-S1 point defense systems that are thought to be capable of detecting and taking down small, slow-moving drones. The system is also thought to be somewhat capable of shooting down incoming mortars and small artillery rockets as well, something Russia says it has done at the base multiple times in the past. That doesn't mean these types of targets couldn't have slipped by, or even that the system was online or in a spot to execute a firing solution at the time of the attack.

The attack itself would seem to raise its own questions about whether Assad's position is truly as stable as it increasingly appeared in 2017. On Dec. 27, 2017, Chief of the Russian General Staff, General Valery Gerasimov, had said that Russia would keep a contingent in Syria for the foreseeable future "to maintain stability and territorial integrity," as well as promote the Kremlin's own interests in the Middle East.

Maksim Blinov/Sputnik via AP

Russian personnel assemble bombs at the country's base in Latakia in 2016.

Regardless, it would be a major achievement for any such group, especially in light of Russian President Vladimir Putin’s visit in which he declared total victory over terrorists in the country. As yet, though, no anti-regime factions, including ISIS or Al Qaeda-linked groups, have claimed responsibility for the attack.

There is also a remote possibility that the incident was actually an accident. Kommersant’s report said the attack had destroyed ammunition storage facility at the base, but this could have been the site of an initial explosion. This would seem unlikely, though, given the Kremlin’s decision to pin the attack on terrorists, despite Putin’s earlier claims about soundly defeating those groups. In addition, on Dec. 31, 2017, an Mi-24 gunship helicopter had crashed in Syria and the Russian government stressed that this had been the result of a technical failure rather than enemy action.

Whatever the case, we will continue to follow this story and provide updates as additional information emerges.